Method and device for monitoring a moving fabric web

ABSTRACT

The invention relates to a method and a device for monitoring a moving fabric web ( 1 ), at least a part ( 7 ) of the width of the fabric web being detected. In order to maintain the geometrical ratios between the individual elements from which the fabric web is constructed as far as possible in the image of the fabric web also, an image of the fabric web is to be produced on the one hand and on the other hand the movement of the fabric web is to be detected in the same part of the fabric web.

The invention relates to a method and a device for monitoring a movingfabric web, at least a part of the width of the fabric web beingdetected.

A device is known from DE 101 23 870 for the automatic monitoring of inparticular textile fabrics or woven fabric webs, this device beingarranged directly on the production machine of the fabric or wovenfabric web. In the case of this device, several very small sensors arearranged having direct contact with the fabric. The device is attachedto the production machine via a vibration-damping suspension, so that atransfer of the machine movement only takes place via the textilefabric.

Although in the case of this device the woven fabric web or the textilefabric is in direct contact with the sensor or its covering glass,faults can occur in imaging of the fabric by the sensor, for exampledisplacements of image sections in relation to one another, which resultin the image of the fabric no longer corresponding to the original. Inthese circumstances it is then difficult to detect faults in the fabricwith certainty, since warp or weft threads, for example, in a wovenfabric are no longer equidistant in the image.

The invention as characterized in the claims thus achieves the object ofproducing a method and a device for monitoring moving fabric webs withat least one sensor strip, which maintains the geometrical ratiosbetween the individual elements from which the fabric web is constructedas far as possible in the image of the fabric web also.

This is achieved in that on the one hand, an image of at least a part ofthe fabric web is produced, and on the other hand the movement of thefabric web is detected in the same part of the fabric web. From theimage of the fabric web a first signal is generated, and in the samepart of the fabric web the movement of the fabric web is detected and asecond signal generated. The first and second signal are offset in asuitable manner in order to maintain in the image also the geometricalratios existing in the fabric web between the individual elements thattogether produce the image.

In a device suitable for this, a sensor strip for scanning the fabricweb seen in the direction of the width of the fabric web can be arrangedat an acute angle, so that information regarding a characteristicconnected with the movement of the fabric web can be derived from thesignal of the same sensor strip. An image of the fabric web in therelevant part is also to be produced from the same signal, this imagebeing built up line-wise or section-wise. However, the sensor strips canalso be oriented perpendicular to the movement of the fabric web and atleast one further sensor for detecting a characteristic connected withthe movement of the fabric web can be arranged in the area of this partof the fabric web. A further sensor of this kind is preferably anoptical sensor with one or more scanning lines.

This method and this device are used in the most common application fordetecting faults in the fabric web, such as differences in thestructure, colour or from patterns on the fabric web, signalling theseor triggering further actions such as stopping of the fabric web, forexample. A particularly important characteristic connected with themovement of the fabric web is its momentary speed, which then appliesprecisely when an image of a section of the fabric web is recorded orproduced.

The advantages achieved by the invention are to be seen in particular inthe fact that, from the signals of the sensor strip and the possiblyadditional signals that a further sensor emits, the geometrical ratiosbetween individual elements of the fabric web, such as between adjacentwarp and weft threads in a woven fabric, for example, can be maintainedeven in the image of the woven fabric produced from signals of thesensor strip. It is easier and also more reliable for example to correctthese geometrical ratios starting out from a momentary speed instead offrom an averaged speed. The further sensor can also only detectdistances, in that it emits a pulse after fixedly predetermineddistances covered, for example, or if supplied externally with clockpulses it outputs the distances covered per clock interval by the fabricweb. With the distance signal and with the signal from the sensor strip,graphic patterns or structures of the fabric web can be reproducedcorrectly and without distortion in the image due to suitable offsettingof both signals, so that interruptions of these patterns or of thestructure can also be detected correctly in the monitoring.

The invention is explained in greater detail below with reference to anexample and to the enclosed figures.

FIG. 1 shows a first diagrammatic representation of an arrangementaccording to the invention of sensor strips and further sensors ahead ofa fabric web,

FIGS. 2, 3, 5 and 6 each show a further arrangement of sensor strips,

FIG. 4 shows an arrangement according to FIG. 1 with further elements,

FIG. 7 shows a distance—time diagram for a fabric web,

FIG. 8 shows a diagrammatic representation of the geometrical ratios onscanning of a fabric web and

FIG. 9 shows a signal such as is possibly generated by sensor stripsaccording to FIG. 2.

FIG. 1 shows ahead of a fabric web 1, the edges of which are indicatedby lines 2 and 3, sensor strips 4 a, 4 b, 4 c, which are formedidentical to one another, as well as further sensors 5 a, 5 b, 5 c,which detect a characteristic of the fabric web that is connected withthe movement of the fabric web 1. Such characteristics are for examplethe distance that the fabric web 1 covers, the momentary speed of thefabric web 1 in the direction in which it is moving, the acceleration inthe event of changes of speed, etc. Each sensor strip 4 and each furthersensor 5 are arranged so that they traverse a part of the fabric web 1when this moves in the direction of an arrow 6 (FIG. 3). Such parts 7 a,7 b, 7 c of the fabric web 1 are delimited in FIG. 1 by further lines 8a, 8 b inside the fabric web 1. The sensor strips 4 a and 4 c and anyfurther sensor strips present and not shown here form a first sensorline 20, while the sensor strip 4 b, alone or together with possiblefurther sensor strips not shown here, forms a second sensor line 21,which runs parallel to the first sensor line 20.

The sensor strips 4 a and 4 c from the first sensor line 20 and thesensor strip 4 b from the adjacent second sensor line 21 partly overlapseen in the direction of movement of the fabric web.

FIG. 2 shows a further arrangement of sensor strips 9 a, 9 b, 9 c andpossible further sensors 10 a, 10 b, 10 c, the sensor strips 9 beinginclined by an angle α, which here for example is 15°, towards a line 11that extends in the direction of the width of the fabric web 1,perpendicular to the direction of the arrow 6.

FIG. 3 shows an arrangement of sensor strips 12 a, 12 b, 12 c accordingto FIG. 1, but with further sensors 13 a and 13 b, which can each beassigned to two sensor strips, as well as further sensors 13 c and 13 d,which are only assigned here to one sensor strip. The further sensors 13a and 13 b are arranged in the edge areas of the sensor strips 12. Itshould be noted here that the arrangements shown with three sensorstrips have been chosen arbitrarily and are only to be interpreted asexamples. Naturally any number of sensor strips 12 can be arranged, thegreater the width the more sensor strips, to detect the entire width ofthe fabric web 1. This applies to all arrangements shown in FIGS. 1 to6. However, it is the case in particular for the arrangement accordingto FIG. 3 that two further sensors are assigned in each case to thesensor strips 12. For example, the further sensors 13 a and 13 b areassigned to the sensor strip 12 b. Further sensors 13 a and 13 c areassigned to the sensor strip 12 c. Further sensors 13 b and 13 d areassigned to the sensor strip 12 c. The sensor strips 12 are arrangedtogether with the further sensors in a housing 18, which also hassuitable lighting for the fabric web 1 if no light source is integratedinto the sensor strips.

FIG. 4 shows an arrangement of the sensor strips 4 a-4 c as alreadyknown from FIG. 1. In contrast to that, however, the further sensors 5a-5 c are no longer connected upstream of the sensor strips 4, butdownstream. This is measured against the direction of movement of thefabric web 1 as indicated by the arrow 6. Lines 14 a, 14 b and 14 cconnect the sensor strips 4 and the further sensors 5 to a processor 15a, 15 b, 15 c respectively, which are connected via lines 16 a, 16 b, 16c to an input/output device 17. Thus several sensor strips and severalfurther sensors are assigned to a common input/output device 17. Anoutput 19 on the input/output device 17 serves for example as aconnection to a computer, such as a so-called PC, to which severaldevices according to the invention can be connected.

FIG. 5 shows an arrangement of five sensor strips 22, 23, 24, 25 and 26,the sensor strips 22, 24 and 26 forming a first sensor line 27 and thesensor strips 23 and 25 forming a second sensor line 28. A furthersensor 29 is assigned here only to the sensor strip 24 and detects apart of the fabric web that is also detected by the sensor strip 24, thesensor strip 24 and the further sensor 29 not scanning the fabric webaccording to the same criteria or detecting the same features therein.

FIG. 6 shows a further arrangement with five sensor strips 30, 31, 32,33 and 34 and five further sensors 35, 36, 37, 38 and 39. Here thefurther sensors are arranged respectively adjacent to the sensor stripsfor which they supply no movement indication. Thus the further sensorsare connected seen in the direction of movement of the fabric web 1alternately upstream and downstream of the assigned sensor strips. Forexample, the further sensor 35 is connected downstream of the relevantsensor strip 30, while the further sensor 36 is connected upstream ofthe relevant sensor strip 31, or vice-versa. This arrangement makes itpossible to fit the sensor strips and the further sensors in aparticularly space-saving arrangement.

FIG. 7 shows a distance-time diagram, for example for the fabric web 1,a line 40 indicating the distance covered per unit of time by the fabricweb 1 with always ideal, uniform movement of the fabric web 1. Thusvalues for the distance covered can be entered along one axis 42 andvalues for the time along an axis 41. A curve 43 represents the distanceactually covered by the fabric web at different times, which distance isproduced by the uneven movement of the fabric web in the area of thesensor strips and further sensors.

FIG. 8 shows in a diagrammatic representation the ratios as they appearwith the arrangement of an inclined sensor strip as shown in FIG. 2. 44here denotes a section through a group of weft threads of a woven fabricthat is moving in the direction of an arrow 45. Slewed by 90° incomparison with the section 44, the centre lines or axes of these weftthreads are drawn in with horizontal lines 46, the warp threads or theirinfluence on these centre lines or axes and thus the weaves being leftout here to make the representation simpler. A sensor strip 47 isrepresented here only by those discrete elements that can detect pictureelements from the fabric web. The sensor strip 47 here is an opticalsensor with a single scanning line. A coordinate system characterizesfurther an X-axis corresponding to the width of the fabric web and aY-axis corresponding to the direction of movement of the fabric web 1.

FIG. 9 shows a first signal 48 and a second signal 49 such as a sensorstrip can emit when it detects a woven fabric. Both signals 48, 49 arerecorded over a time axis T and next to an axis V, the axis V indicatingthe amplitude of the signal from the sensor strip, which is expressedfor example by an electric voltage.

The mode of operation of the invention is as follows: While for exampleone sensor strip 4 a (FIG. 4) scans the part 7 a of the fabric web 1 andmaps this onto picture elements and converts it into intensity values,or into grey scale and colour values, which are stored in the memory ofthe processor 15 a, the further sensor 5 a continuously emits a signalto the processor 15 a, which represents for example the momentarymovement of the part 7 a of the fabric web 1 in the area of the sensorstrip 4 a. The further sensor 5 a traverses a section inside the part 7a of the fabric web 1. This applies likewise to the further sensors 5 b,5 c and the parts 7 b, 7 c of the fabric web 1. The processors 15contain a program in the program memory that recognizes periodicities orprojecting signal portions from the signal of the sensor strip andprocesses these together with the signal from the further sensor. Theaim of this program is to form a clearly structured signal or a clearimage from the signal of the sensor strip. The object should thus forexample be achieved that in an image that can be composed from thepicture elements in the data memory of a processor 15, in a textilefabric the geometrical relationships between the individual yarns orthreads are preserved such that they correspond to those of the actualfabric. In the case of woven fabrics, the structure from the warpthreads and the weft threads should thus be made clearly recognizable.Original distances or geometrical ratios between warp and weft threadsof a woven fabric or between threads of a knit fabric should bereproduced in the image. Due to the further sensors arranged as closelyas possible to and in the working area of the sensor strips on thefabric web 1, it is possible to detect even local movements that aredifferent in the individual parts 7 a-7 c, such as e.g. distortion, andto compensate for them, i.e. to ensure that the effect of the distortiondoes not geometrically distort the image from the sensor strip. Inparticular, the further sensors 5, 10, 13, 29, 35-39 detect the movementof the fabric web 1 as shown for example in FIG. 7. From this it isrecognized that the fabric web does not always cover identical distancesper unit of time. Thus the images that the sensor strips 4, 9, 12 and22-26 detect can even contain not always the same number of elementssuch as threads, weft threads, etc. If this image information iscombined with the signal relating to the movement for example from thefurther sensor, a faithful image of the fabric web can be produced evenif its movement is uneven.

If no further sensor is used and if a characteristic connected with themovement of the fabric web is to be detected by the sensor strip alone,then the latter must be inclined by an angle α, as shown in FIG. 2. Themovement of the fabric web can be detected as shown with reference toFIGS. 8 and 9. As an example, we are assuming here that the fabric webhas a three-dimensional structure such as applies to textile fabrics,and that it moves in the direction of an arrow 45. If we look at themovement of a single weft thread 50, which is also represented by itscentre line or axis 51, then a curve is produced for example for theintensity of light that is reflected at this or absorbed by this,corresponding to a signal 48 (FIG. 9). The signal 48 is produced inparticular by a point or a surface line 52 of the weft thread 50, whichis also represented by the centre line 51, passing by a sensor element53, the sensor element 53 being able to generate a picture element,meaning that in this picture element the intensity progressescorresponding to the signal 48. If a short time later the weft thread 50reaches a place (shown here moved forward for greater clarity) in thedirection of the arrow 45 as designated by 54, which corresponds to aposition of the centre line corresponding to a dashed line 55, then anadjacent sensor element 56 detects this weft thread in its position 54,a signal 49 according to FIG. 9 being produced, which is delayed by atime Δt relative to the signal 48. However, since a distance ΔL betweenthe sensor elements 53 and 56 or centre lines 51 and 55 is known, themomentary speed v of the fabric web 1 is found according to the formulav=ΔL/Δt. However, it is also possible to calculate from this even theacceleration, for example, as another characteristic that is connectedwith the movement of the fabric web.

The movement of the fabric web 1 or a characteristic connected with themovement of the fabric web can also be ascertained from the overlappingsensor strips, as shown for example in FIG. 3. In the overlapping areaof the sensor strips 12 a and 12 b, which is located before and afterthe further sensor 13 a that is drawn in here but not required in thiscase, the same parts of the fabric web 1 are detected and thuscomparable signals produced, which occur, however, with a delay thatcorresponds to the distance between the two sensor strips 12 a and 12 bdivided by the speed of the fabric web 1 in this area. Since thedistance is known and the delay can be determined from both signals, thespeed can be calculated from this.

Sensors known by the designation “contact type image sensor”, forexample, such as are installed in a flatbed scanner or a fax machine forscanning a piece of paper supplied, can be used as sensor strips 7, 9,12. In this case the sensors can contact the fabric web directly, orthey are covered by a cover plate for example of glass, which is touchedby the fabric web. A small air gap can also separate the fabric web andthe sensor from one another. It is possible also to use surface camerasor line cameras instead of the said contact sensors or sensor strips,which cameras then scan a rather larger area of the fabric web seen inthe direction of the arrow 6. The further sensor 5, 10, 13 can be asensor such as is known for example by the name “CMOS Active Pixel ImageSensor” supplied by National Semiconductor. Even a further sensor suchas supplied by Agilent Technologies under the name ADNS-2051 OpticalMouse Sensor can be used.

1. Method for monitoring a moving fabric web, at least a part of thewidth of the fabric web being detected, wherein on the one hand an imageof the fabric web is produced and on the other hand the movement of thefabric web is detected in the same part of the fabric web.
 2. Device forexecuting the method according to claim 1, wherein a sensor strip isarranged inclined at an angle to the fabric web, and thus on the onehand an image of the fabric web is produced and on the other hand acharacteristic connected with the movement of the fabric web is detectedin the area of this part of the fabric web.
 3. Device for executing themethod according to claim 1, wherein apart from a sensor strip, withwhich an image of the fabric web is produced, at least one furthersensor for detecting a characteristic connected with the movement of thefabric web is arranged in the area of this part of the fabric web. 4.Device according to claim 3, wherein seen across the width of the fabricweb, several sensor strips are arranged each with a further sensor, thesensor strips being arranged behind one another in the direction of thewidth of the fabric web and forming a sensor line.
 5. Device accordingto claim 4, wherein at least two substantially parallel sensor lines arearranged relative to the fabric web.
 6. Device according to claim 4,wherein a sensor strip from a first sensor line and a sensor strip froman adjacent second sensor line partly overlap seen in the direction ofmovement of the fabric web.
 7. Device according to claim 6, wherein asensor strip from the adjacent sensor line is provided as a furthersensor, a characteristic connected with the movement of the fabric webbeing acquired from the signals of the two overlapping sensor strips. 8.Device according to claim 6, wherein a further sensor is arranged in thearea of overlap of the two sensor strips.
 9. Device according to claim5, characterized in that wherein in each sensor line a further sensor isarranged next to a sensor strip seen in the direction of the width ofthe fabric web.
 10. Device according to claim 3, wherein the furthersensor is an optical sensor with several scanning lines.
 11. Deviceaccording to claim 3, wherein the sensor strip is an optical sensor withone scanning line.
 12. Device according to claim 3, wherein the sensorstrip is a so-called contact image sensor such as is used in a flatbedscanner.
 13. Device according to claim 2, wherein a processor, which isconnected to an input/output device, is assigned to the sensor strip.14. Device according to claim 11, wherein a common input/output deviceis assigned to several sensor strips and several further sensors. 15.Method according to claim 1, wherein a first signal is generated fromthe image of the fabric web and in the same part of the fabric web themovement of the fabric web is detected and a second signal is generated,and the first and the second signal are offset in a suitable manner, inorder to produce original geometrical ratios, such as graphic patternsand structures of the fabric web, in the image also.